Swedish Radio's South Asia correspondent, Nils Horner, has been killed in Afghanistan.

He was shot dead in broad daylight on a Kabul street, close to a Lebanese restaurant where a bomb went off in January earlier this year. He was doing interviews at the time, ahead of the upcoming elections in Afghanistan.

He was shot in the back of the head, and pronounced dead at a Kabul hospital. A witness spoke to news agency Reuters and described hearing a single gunshot fired before seeing Nils Horner, who had been talking to his interpreter, fall to the ground, and two men in military uniform run away. Sources close to the Taliban claim they were not responsible for the shooting.

The 51-year-old, who had worked in the region for many years, had been in touch with colleagues back at Broadcasting House in Stockholm on the morning he was killed. "He was in contact with staff before he left for interviews and then there was a news bulletin shortly after 8 a.m. our time, claiming that a foreign person had been shot. Our staff at home then called Nils' mobile and a man picked up the phone who turned out to be a doctor at the hospital where they had brought Nils, and he told us that he had been shot in the back of the head and was dead," Swedish Radio's Director-General Cilla Benkö told Radio Sweden.

"We mourn a dear and esteemed colleague, but it is to Nils' family that our thoughts are with today," said Swedish Radio foreign correspondent and colleague, Agneta Ramberg.

"If someone knew and could be extremely safety conscious, it was Nils. He had a huge experience and used that knowledge. He had also been in Kabul, many, many times before and knew all about the security situation there. But this, to be suddenly shot in the street, no one can protect against," Agneta Ramberg said.

Nils Horner had reported from Afghanistan in 2001 when the Taliban were forced from power, during the USA's entry into Baghdad in 2003, from Thailand following the Tsunami in 2004, and from Japan after the tsunami and ensuing Fukushima nuclear plant disaster in 2011. Later back in Stockholm in 2011, he told Radio Sweden about his attitude towards his own safety in the world's trouble spots when grabbing a story.

"Most journalists are not interested in risking their lives for a story, some do, but I don't think it's in our culture here at Swedish Radio to take insane risks to do the story and also as radio journalists we don't have to be extremely close to people shooting.

"As a TV cameraman they have to be very close to get the pictures but we don't feel the same pressure to be always in the middle of some firefight or something but of course we want to be as close as possible and in Japan, I wanted to come close to the people who were thinking of whether they should evacuate or not, so you almost have to ask yourself everyday, is it worth taking the risk or is it not?" Nils Horner said to Radio Sweden.

Nils Horner worked during the 1990s as a journalist in London and New York. He started work as a foreign correspondent for Swedish national radio in 2001.

Swedish Radio's Director-General Cilla Benkö says this is one of the worst days in the corporation's history.

"Nils was one of our absolute best and most experienced correspondents and what has happened to him today is terrible. We are now trying to get as many details as we can", she said in a statement.

"We know there are high-risk areas", she said, "Kabul isn't an area Swedish Radio should not cover."

According to journalists in Kabul, Hong Kong-based Horner arrived in Afghanistan on Sunday and had planned to stay about a week or 10 days. "Among Swedish journalists, he was a legend," Johan Nylander, a Swedish freelance journalist based in Hong Kong, told news agency AFP.

"For many years, he didn't even have an apartment. Hong Kong was the first place he put down his suitcase for half a decade."

Swedish Prime Minister Fredrik Reinfeldt passed on his sympathies at a press conference: "I want to express my deepest condolences to Nils Horner's relatives", he said, "we know Nils Horner as a knowledgeable, enthusiastic and experienced journalist. Many Swedes have listened to his voice, a voice which has now been silenced."